1. Field of the Invention
The present invention relates to a backlight system disposed in a back side of a liquid crystal display.
2. Description of Related Art
Recently, liquid crystal displays each including a backlight system have become widely used in various electronics items such as notebook computers in which optical communication devices are installed, personal digital assistants, mobile phones, liquid crystal televisions or the like.
It is known that this kind of backlight system includes a light-emitting source such as a fluorescent lamp or an LED, and a light diffusion plate configured to uniformly diffuse light emitted from the light-emitting source to illuminate the liquid crystal display. This kind of backlight system uniformly illuminates the liquid crystal display from a back side thereof, and has the advantageous effects that a person can look easily at the liquid crystal screen and also the backlight system itself can be thinned.
An LED is often used as the light-emitting source of the backlight system, and hence a miniaturized, thinned and long-lived backlight system can be achieved. If LEDs are used and it is desired to acquire white illumination light from the backlight system, three kinds of high-intensity LEDs, red (R), green (G) and blue (B) LEDs, are used, and these three kinds of LEDs are simultaneously lighted or lighted in a time sharing manner. The light from the three kind of LEDs is mixed and this mixed lights appears to be white light. White-light emitting LEDs comprising blue LEDs and fluorescent materials may be used instead of RGB LEDs. Each of the white-light emitting LEDs emits white light singularly.
In particular, if white-light emitting LEDs are used in a backlight system, a structure of the backlight system is simplified, and miniaturization of the backlight system is also accomplished.
FIG. 4 illustrates a conventional backlight system as disclosed in Japanese Utility Model Laid-Open No. S64-49886, for reference. The backlight system 1 includes an insulative printed board 2, a plurality of LEDs 3 disposed on an upper surface of the printed board 2, a reflective frame 4 disposed to surround the plurality of LEDs 3, and a light diffusion member 5 mounted on an upper end surface of the reflective frame 4 to face a light-emitting surface (upper surface) of each of the LEDs 3. The backlight system 1 is disposed close to a back surface of a liquid crystal display 7. Moreover, a white glossy film 6 is printed on a surface of the printed board 2 excepting the LEDs 3 and configured to reflect light emitted from the LEDs 3 upwardly.
With the backlight system 1 having the structure as mentioned above, most of the illumination light from the LEDs 3 enters the light diffusion member 5 and becomes scattered light which is emitted in the direction of the liquid crystal display 7. In this case, one portion of the illumination light is reflected by the light diffusion member 5 to be returned to the printed board 2, the returned light is reflected on the white glossy film 6 printed on the surface of the printed board 2 upwardly, and the light reflected by the film again enters the light diffusion member 5 and is thereafter emitted to the liquid crystal display 7.
However, in the backlight system 1 structured as mentioned above, if the backlight system is used for a large-size liquid crystal display, because a large-size printed board 2 must be used depending on the large-size screen of the liquid crystal display, there is a problem that the weight of the printed board 2 becomes excessive, resulting in a low practical value for the backlight system.